Copper-based Oxides Research Articles

Electron states in the two-band Hubbard model: Paramagnetic phase

The electron energy spectrum of the copper-based oxides is calculated in the two-band Hubbard model. The conditions for the onset of a localized spin state are studied. The effect of doping is also studied.

Hydrogen Species, Vacancies, and Alkadiene Hydrogenation Selectivity on Copper-Based Hydrogen Reservoirs

Hydrogenation of 2-methylbuta-l,3-diene (isoprene) under helium flow in the absence of gaseous hydrogen is used to provide evidence for reactive hydrogen species (H*) present in copper-based oxides (CuCrO, CuAlO, CuZnO). These compounds are hydrogen reservoirs with marked diffusion properties for hydrogen species (H*, OH−). Moreover, analysis of the distribution of hydrogenated products obtained under H2 + isoprene in relation to the solid structure of the catalyst leads to the proposition of particular active sites, XM-YM′. These are constituted of two cations: XM is the 3-coordinatively unsaturated Cu+ ion and YM′ is a second cation (Cr3+, Al3+, Zn2+) with Y unsaturations of coordination. Under H2 a high degree of unsaturation can exist (3M-3M′), whereas under helium a change in the selectivity of hydrogenated products is observed that is attributed to the variation of Y (3 down to 0). This phenomenon corresponds to a progressive blocking of the surface unsaturations, probably due to the migration of OH− groups.

Bipolaron kinetics of high-Tc metal oxides: Hall effect, resistivity and 'spin' gap

A normal-state kinetic theory of copper-based oxides, which is an extension of BCS theory and Anderson localization to the strong-coupling limit lambda >1, is proposed. In this limit carriers are charged 2e bosons (small bipolarons) below and above Tc. Temperature and doping dependencies of resistivity and Hall effect in copper oxides are explained by taking into account the localization of charged bosons in a random potential. Links with the 'spin' gap, high Tc and with some other unusual properties are discussed.

Crystal chemistry of copper-based oxide superconductors and related compounds

We propose a new method for the classification of the copper oxide superconductors and their related compounds in terms of the crystal structure. This method is based on the combination of four different groups of structural-unit blocks, i. e. perovskite (ACuO 3−z), rock-salt (AO), fluorite (AO 2) and cesium chloride (AX) blocks. A variety of new layered copper oxides which may turn into new high-T c superconductors can be designed by employing the basic principles of the present block model and taking into account the lattice constant matching and the electroneutrality condition between the blocks.

Crystal Chemistry of Copper-Based Oxide Superconductors and Related Compounds

Abstract We propose a new method for the classification of the copper oxide superconductors and their related compounds in terms of the crystal structure. This method is based on the combination of four different groups of structural-unit blocks, i. e. perovskite (ACuO 3−z ), rock-salt (AO), fluorite (AO 2 ) and cesium chloride (AX) blocks. A variety of new layered copper oxides which may turn into new high-T c superconductors can be designed by employing the basic principles of the present block model and taking into account the lattice constant matching and the electroneutrality condition between the blocks.

特集 原子層制御から原子制御へ ９． 各種材料の層状成長 ９．１ 高温超伝導薄膜結晶の原子層成長

The mechanism and the method of atomic layer growth of copper-based oxide superconducting thin films are discussed. Taking advantage of the two dimensional layered structure of high-Tc superconductors, these layered structures have been constructed by a layer-by-layer deposition method using laser MBE method. The basic structural parameters based on the CuO2 sheets have been successfully changed to control the high-Tc superconductivity with these methods.

A comparison of the oxygen evolution upon acid dissolution of Ba0.6K0.4BiO3, with the copper-based oxides LaCuO3 and La1.85Sr0.15CuO4

Abstract Gas chromatography/mass spectrometry was used to analyze the oxygen evolved from Ba 0.6 K 0.4 BiO 3 , LaCuO 3 and La 1.85 Sr 0.15 CuO 4 upon dissolution in normal and 18 O-enriched acid. From the 18 O/ 16 O ratio we show that the oxide phases are the principal source of evolved oxygen in the copper-containing materials, while more than half of the oxygen is evolved from the solution with Ba 0.6 K 0.4 BiO 3 . The difference may be due to the location of the holes, which appear to be predominantly on the oxygens in the copper-based materials and on the Bi(Bi V) in Ba 0.6 K 0.4 BiO 3 .

Preface

Since the discovery of the phenomenon of superconductivity in mercury by Heike Kammerlingh Onnes in 1911, the search for new compounds with higher transition temperatures has presented a continuous challenge in the field of materials science. After the discovery of the Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn superconductors with A 15-type structure, the efforts, mainly concentrated on intermetallic compounds, experienced steady but slow success. With a T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> of 23.3 K in Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Ge, however, a limit seemed to have been approached. Reports of materials with higher T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> appeared occasionally, but these could not withstand the critical tests. Superconductivity research was just celebrating its 75th anniversary in 1986, when interest in the field was sparked by the discovery of a new class of metallic perovskite-type copper-based oxides with transition temperatures of 35 K.